/**
 * 
 */
package niuke;

import java.util.Scanner;

/**
 * @author zhongfang
 *
 */
public class 轮回期望 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		Scanner scanner=new Scanner(System.in);
		int n=scanner.nextInt();
		double v=scanner.nextDouble();
		double u=scanner.nextDouble();
		double[] c=new double[n];
		double[] d=new double[n];
		for (int i = 0; i < n; i++) {
			c[i]=scanner.nextDouble();
		}
		for (int i = 0; i < n; i++) {
			d[i]=scanner.nextDouble();
		}
		double result=0;
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < n; j++) {
				result+=1/(c[i]-j*d[i]-v);
			}
		}
		
		result*=u;
		System.out.println(String.format("%.3f",result));
		
	}

}
